A molecular model for the line tension of lipid membranes

The line tension of a symmetric, lipid bilayer in its liquid-crystalline st ate is calculated on the basis of a molecular lipid model. The lipid model extends the opposing forces model by an expression for the conformational f ree energy of the hydrocarbon chains. We consider a membrane edge that cons ists of a perturbed bilayer covered by a section of a cylinder-like micelle . The structural rearrangement of the lipids implies an excess: free energy which we minimize with respect to the cross-sectional shape of the membran e edge, including both the micellar and the bilayer region. The line tensio n is derived as a function of molecular lipid properties, like the lipid ch ain length or the head group interaction strength. We also relate it to the spontaneous curvature of the lipid layer. We find the line tension to beco me smaller for lipid layers that tend to curve more towards the hydrophobic core. Our predictions for the line tension and their relation to experimen tally derived values are discussed.